Permeability properties of ENaC selectivity filter mutants.
Permeability properties of ENaC selectivity filter mutants.
复制标题
ENAC选择性滤波器突变体的渗透性特性。
DOI：
10.1085/jgp.118.6.679
复制
发表时间：
2001-12
影响因子：
3.8
通讯作者：
Schild, L
中科院分区：
文献类型：
--
作者：
Kellenberger, S;Auberson, M;Gautschi, I;Schneeberger, E;Schild, L
上皮Na+通道（ENaC）位于紧密上皮细胞的顶膜，允许Na+吸收。阿米洛利敏感的ENaC对Na+和Li+离子具有高度选择性。越来越多的证据表明，在推定的第二跨膜结构域M2之前的氨基酸残基（preM 2）的短延伸形成具有阿米洛利结合位点的外通道孔和孔的窄离子选择性区域。我们之前已经证明，前M2片段中αS589残基的突变改变了离子选择性，使通道对K+离子具有渗透性。为了理解这种重要的离子选择性变化的分子基础，我们用不同大小和物理化学性质的氨基酸取代了αS589。在这里，我们表明无机和有机阳离子通道孔的分子截止随着α589位氨基酸残基的大小而增加，这表明αS589突变扩大了选择性过滤器的孔。具有增加的对大阳离子的渗透性的突变体显示小阳离子如Na+和Li+的ENaC单位电导的降低。这些发现证明了αS589残基处的孔径对于ENaC的选择性性质的关键作用。我们的数据与选择性过滤器通道孔内衬αS589残基的主链羰基氧一致，其侧链指向远离孔腔。我们提出αS589侧链朝向亚基-亚基界面，并且αS589被较大残基取代通过在亚基-亚基界面处增加额外体积来增加孔径。
The epithelial Na+ channel (ENaC), located in the apical membrane of tight epithelia, allows vectorial Na+ absorption. The amiloride-sensitive ENaC is highly selective for Na+ and Li+ ions. There is growing evidence that the short stretch of amino acid residues (preM2) preceding the putative second transmembrane domain M2 forms the outer channel pore with the amiloride binding site and the narrow ion-selective region of the pore. We have shown previously that mutations of the αS589 residue in the preM2 segment change the ion selectivity, making the channel permeant to K+ ions. To understand the molecular basis of this important change in ionic selectivity, we have substituted αS589 with amino acids of different sizes and physicochemical properties. Here, we show that the molecular cutoff of the channel pore for inorganic and organic cations increases with the size of the amino acid residue at position α589, indicating that αS589 mutations enlarge the pore at the selectivity filter. Mutants with an increased permeability to large cations show a decrease in the ENaC unitary conductance of small cations such as Na+ and Li+. These findings demonstrate the critical role of the pore size at the αS589 residue for the selectivity properties of ENaC. Our data are consistent with the main chain carbonyl oxygens of the αS589 residues lining the channel pore at the selectivity filter with their side chain pointing away from the pore lumen. We propose that the αS589 side chain is oriented toward the subunit–subunit interface and that substitution of αS589 by larger residues increases the pore diameter by adding extra volume at the subunit–subunit interface.